The present invention relates to a rotor for a rotary fluid pump or compressor and to a method for its manufacture. Rotary compressors having a rotor assembly supported by a shaft must be carefully designed because of the relatively high local stresses where the shaft abuts the rotor and the rotation of such a rotor subjects this portion of the device to alternating loads that can induce fatigue fracture. While strengthening that portion of the device would alleviate such a problem, the fact that it is desirable from several standpoints to reduce the weight of the rotor makes overdesign of the rotor/shaft interface an undesirable solution to the problem.